new how-to: reduce to construct JSON (#4160)

new how-to: reduce to construct JSON Co-authored-by: Anais Dotis-Georgiou <anais@Anaiss-MacBook-Pro.local> Co-authored-by: kelseiv <47797004+kelseiv@users.noreply.github.com>
2022-07-07 13:09:17 -05:00 · 2022-07-07 13:09:17 -05:00 · bea34af485
parent 5cd87a623e
commit bea34af485
1 changed files with 69 additions and 0 deletions
--- a/content/resources/how-to-guides/reduce-to-construct-JSON.md
+++ b/content/resources/how-to-guides/reduce-to-construct-JSON.md
@ -0,0 +1,69 @@
+---
+title:  Using reduce() to construct a JSON. 
+description: >
+  Learn how to send multiple points with `http.post()` by creating a JSON object with `reduce()`. 
+menu:
+  resources:
+    parent: How-to guides
+weight: 105
+---
+
+## Send data in JSON body with `http.post()`
+Use the [reduce()](/flux/v0.x/stdlib/universe/reduce/) function to create a JSON object to include as the body with `http.post()`. 
+
+1. Import both the [array](/flux/v0.x/stdlib/array/) package to query data and contruct table(s), and the [http package](/flux/v0.x/stdlib/http/) to transfer JSON over http.
+2. Use `array.from()` to query data and construct a table. Or, use another method [to query data with Flux](/influxdb/v2.3/query-data/flux/). 
+3. Use the `reduce()` function to construct a JSON object, and then use `yield()` to store the output of reduce. This table looks like: 
+
+    | field                 | tag                            |
+    | :-------------------- | :----------------------------- |
+    | example-field:["3"4"1 | {example-tag-key:["bar"bar"bar |
+
+4. Use the [map()](/flux/v0.x/stdlib/universe/map/) function to combine the two components together into a JSON object, and then use a second `yield()` function to store this object as `final JSON`. This table looks like:
+
+    | field                 | tag                            | final                                                     |
+    | :-------------------- | :----------------------------- | :-------------------------------------------------------  |
+    | example-field:["3"4"1 | {example-tag-key:["bar"bar"bar | {example-tag-key:["bar"bar"bar] , example-field:["3"4"1]} |
+
+5. Use the `findRecord()` function to extract the value from the final column, the JSON. 
+6. Use `http.post()` to specify a URL to sent the JSON to. In this example, we use [Post Test Server](https://ptsv2.com/) as URL to send the JSON to, and test the `http.post()` function. 
+
+```js
+import "array"
+import "http"
+
+ 
+data = array.from(
+        rows: [
+            {_time: 2020-01-01T00:00:00Z, _field: "example-field", _value: 3, foo: "bar"},
+            {_time: 2020-01-01T00:01:00Z, _field: "example-field", _value: 4, foo: "bar"},
+            {_time: 2020-01-01T00:02:00Z, _field: "example-field", _value: 1, foo: "bar"},
+        ],
+    )
+  
+    |> reduce(
+            fn: (r, accumulator) => ({tag:accumulator.tag + "\"" + r.foo, 
+                                    field : accumulator.field + "\"" + string(v:r._value)
+                                    }),
+            identity: {tag: "{example-tag-key:[", 
+                    field: "example-field:[" }
+    )
+    |> yield(name: "output of reduce")
+    |> map(fn: (r) => ({ r with tag: r.tag + "]" }))
+    |> map(fn: (r) => ({ r with field: r.field + "]}" }))
+    |> map(fn: (r) => ({ r with final: r.tag + " , " + r.field}))
+    |> yield(name: "final JSON")
+    |> findRecord(
+        fn: (key) => true,
+        idx: 0,
+        )
+
+
+http.post(
+    url: "https://ptsv2.com/t/c4x38-1656014222/post",
+    headers: {"Content-type": "application/json"},
+    data: bytes(v: data.final),
+    )
+```
+
+